October 2, 2013

Flowering Plants Evolved 100 Million Years Earlier Than Believed

Researchers from the University of Zurich in Switzerland have uncovered evidence suggesting flowering plants evolved 100 million years earlier than previously believed, according to new research appearing in the open-access journal Frontiers in Plant Science.

Flowering plants evolved from extinct plants related to conifers, cycads, ginkgos and seed ferns, and the oldest known fossils from these types of plants are pollen grains – small, robust spores which are numerous and fossilize more easily than flowers or leaves. Now, drilling cores have unearthed well-preserved 240-million-year-old pollen grains, making them the oldest known fossils from flowering plants.

“An uninterrupted sequence of fossilized pollen from flowers begins in the Early Cretaceous, approximately 140 million years ago, and it is generally assumed that flowering plants first evolved around that time,” the university explained in a statement.

“But the present study documents flowering plant-like pollen that is 100 million years older, implying that flowering plants may have originated in the Early Triassic (between 252 to 247 million years ago) or even earlier,” it added. “Many studies have tried to estimate the age of flowering plants from molecular data, but so far no consensus has been reached. Depending on dataset and method, these estimates range from the Triassic to the Cretaceous.”

Typically, molecular estimates need to have a foundation based on fossil evidence, the researchers explained. However, when it came to flowering plants, exceptionally old fossils had not been available. This is the reason why the Zurich team’s discovery of flower-like pollen dating back to the Triassic is said to be so significant.

Study authors Peter Hochuli and Susanne Feist-Burkhardt analyzed a pair of drilling cores obtained from Weiach and Leuggern in northern Switzerland. They discovered pollen grains resembling fossil pollen from the earliest known flowering plants, and then used laser-scanning microscopy to obtain high-resolution 3D images of six different types of pollen.

Nine years ago, the duo conducted research in which they described different but related flowering plant-like pollen from the Middle Triassic in cores from the Barents Sea, south of Spitsbergen. That study, combined with the results of their current work, leads Hochuli to conclude “even highly cautious scientists will now be convinced that flowering plants evolved long before the Cretaceous.”

“What might these primitive flowering plants have looked like? In the Middle Triassic, both the Barents Sea and Switzerland lay in the subtropics, but the area of Switzerland was much drier than the region of the Barents Sea,” the university said. “This implies that these plants occurred a broad ecological range. The pollen's structure suggests that the plants were pollinated by insects: most likely beetles, as bees would not evolve for another 100 million years.”